Turkey is not satisfied in talks with the U.S. on establishing a "safe zone" in northern Syria and will act alone if there is no progress, Foreign Minister Mevlut Cavusoglu said on Friday.

The two countries have started joint land and air patrols along part of Syria's border with Turkey, but Ankara remains angry with Washington's support for the YPG, which has been a key ally in its fight against the Islamic State in Syria, but is deemed a terrorist group by Turkey.

The security zone is designed to be off-limits to the YPG and is expected to provide settlement for some of the 3.6 million Syrians who fled their country's civil war.

"We are not pleased with the current state of efforts and we have conveyed this to the Americans very clearly," Cavusoglu told reporters after the U.N. General Assembly in New York.

Ankara has repeatedly threatened to act against the Syrian Kurdish YPG militia, unless the U.S. removes the fighters from a 480-kilometer long area on the Syrian side of its border.

On the sidelines of the General Assembly, U.S. Special Envoy to Syria James Jeffrey told reporters that Washington was moving as fast as possible. 

"We've made it clear to Turkey at every level that any unilateral operation is not going to lead to an improvement in anyone's security ... The Turks have an option, of course, to act militarily."

The protracted Syrian civil war is entering eight-and-a-half years. After many rounds of talks to end the war had failed, the U.N. announced last week the formation of a constitutional committee for Syria, a long-awaited step in a stalled peace process.

The body will comprise 150 people, split three ways between the government, opposition and civil society, with each side selecting 15 people to prepare and draft constitutional proposals.

U.N. officials say such a committee is key to political reforms and new elections meant to unify Syria and end a war that has killed hundreds of thousands and displaced about half of its population.

(With input from Reuters)